Curtain walls, building facades, store fronts, windows, glazed doors, decorative and utility glazing and the like, generally known as fenestration products, are typically made with aluminum framework. Aluminum is favored because of its light weight combined with good strength and extrudability. The fenestration art has struggled, however, with the relatively high thermal conductivity of aluminum, which tends to reduce thermal efficiency in all climates.
One widely accepted solution to the thermal conductivity problem has been to introduce one or more members having low thermal conductivity between internal and external aluminum parts; often the inserted member is made of a synthetic polymer having a low thermal conductance. For example, glass fiber reinforced polymers of various kinds have been extruded to form such inserts. The industry uses the term “thermal break” to mean a piece of material having a low thermal conductivity that is inserted between high conductivity members in order to reduce heat transfer from one side of a structure to another. One recognized standard is that the thermal break material conductivity should not be more than 0.52 W/mK (3.60 Btu·in/h·ft2−° F.); however, usage of the term “thermal break” herein is not intended to be limited to this standard, nor is it necessarily a piece inserted between others—in this context it may be attached to only a single member with high thermal conductivity.
The most energy efficient and ideal design would be one where thermal conductivity from the exterior to interior (or interior to exterior) of a building is zero. While this has not yet been achieved, there is an ever-present demand for improved thermal performance. One solution to decreasing thermal conductivity via a thermal break is increasing the size or length of the thermal break. However, as thermal breaks typically are not manufactured with the strength required to bear the load that other fenestration elements bear; therefore, enlarging the thermal break member may decrease the overall structural integrity of the fenestration assembly of which it is part.
Other components of the fenestration—doors, windows, and infill, such as glazing—bear a weight load of the fenestration assembly. The components also are subjected to other stressors, such as wind (“wind load”), which can impart notable torque and pressure changes on the glazing and other parts of the fenestration assembly. Infill must not merely be held in place, but must be able to withstand wind load. To assist in securing infill, various styles of retainers, sometimes known as pressure plates, have been developed to assure the integrity of the installation.
Each element of a conjoint fenestration unit, particularly those on the external side, is subjected to weather, including changes in temperature. Thus, consideration must also be taken in choosing suitable materials for conjoining elements at their intersection. As noted above, strength and thermal conductivity may be considered, but thermal expansion also contributes to the overall integrity of the conjoint fenestration unit. When conjoining different materials, their different thermal expansion properties will cause the conjoining elements to expand differently thus changing the strength of the connection between said conjoining elements.
Finally, thermal breaks are typically manufactured separately from other fenestration products and thus must be fastened to the other parts during assembly, for example, with clips or other fastening mechanisms. Pressure plates (and other retainers), thermal breaks and all other required parts (e.g., gaskets, clips) form a list of parts cumbersome to inventory and assemble. Generally, the more parts there are to install, the more labor is required, and the possibility of faulty assembly is increased.
Thus, driven by the need for both simplified assembly and increased thermal performance, the present invention aims to reduce the number of parts in the fenestration assembly, to maintain or improve the ability to withstand wind load and other stresses, and to maintain or improve thermal performance, thereby reducing both manufacturing and installation costs.